chore: add server provisioning migrations

- 003_add_server_tables.sql: server_orders, server_instances tables
- 003_server_sessions.sql: KV-based session tracking
- 004_add_terminated_at.sql: track instance termination time

Co-Authored-By: Claude Opus 4.5 <noreply@anthropic.com>

migrations/003_server_sessions.sql

@@ -0,0 +1,17 @@
+-- Server consultation sessions table
+CREATE TABLE IF NOT EXISTS server_sessions (
+  user_id TEXT PRIMARY KEY,
+  status TEXT NOT NULL DEFAULT 'gathering',
+  collected_info TEXT,  -- JSON
+  last_recommendation TEXT,  -- JSON  
+  messages TEXT,  -- JSON
+  created_at INTEGER NOT NULL,
+  updated_at INTEGER NOT NULL,
+  expires_at INTEGER NOT NULL
+);
+
+-- Index for cleanup job
+CREATE INDEX IF NOT EXISTS idx_sessions_expires ON server_sessions(expires_at);
+
+-- Index for status queries
+CREATE INDEX IF NOT EXISTS idx_sessions_status ON server_sessions(user_id, status);